Decomposition of buried cellulose film, with special reference to the ecology of certain soil fungi

DECOMPOSITION OF BURIED CELLULOSE
FILM, WITH SPECIAL REFERENCE TO THE
ECOLOGY OF CERTAIN SOIL FUNGI

H. T. TRIBE
School of Agriculture, Cambridge

In a discussion on decomposition of organic matter in soil, considera-
tion of the break-down of cellulose is of some importance, since cellu-
lose in a number of forms is continually being added to soils. For ex-
ample, plant residues containing structural cellulose become incorpor-
ated into arable soils during agricultural operations, and cellulose is also
incorporated into these soils in farmyard manure. In the form of leaf
litter, cellulose is added to forest soils, though here the conditions for
decomposition differ in that successive layers of leaves are deposited
one upon the other on the soil surface, whilst in the former examples the
cellulose is intimately mixed with the soil. Cellulose in these forms is
associated with many other materials of, for example, lignin, cutin, or
protein nature. A microflora may be already present on these cellulose-
containing substrates before they reach the soil. The analysis of the
natural decomposition process is therefore very complicated. In the
work on which this paper is based (Tribe, 1957), cellulose film, washed
and sterilized before burial, was used as a substrate on which to follow
microbial development. Grade PT 300 ‘Cellophane’, kindly supplied
by the British Cellophane Company, Bridgwater, Somerset, is a pure
form of cellulose and its transparency renders it a perfect substrate
on which to observe soil organisms under the microscope. The absence
of encrusting materials from the film may result in a poorer fungus
flora than is normally found on cellulosic plant residues. A number of
fungi however developed readily on cellulose film. The mineral nutrients
and perhaps growth factors were presumably supplied from the soils in
which the film was buried.

The technique of study of buried cellulose film is simple. Pieces of washed ‘Cello-
phane’ of c. 0-5 x 1:0 cm. were damped in sterile water and placed singly on
4 in. cover slips, to which they adhered, and the cover slips buried vertically in
soil. On recovery, the microbial material colonizing the cellulose was stained in

picronigrosin in lactophenol (Smith, 1954), which did not stain the cellulose.
Permanent preparations were made in lactophenol. Certain isolations of fungi were

DECOMPOSITION OF BURIED CELLULOSE FILM 247

made from cellulose immediately after its removal from soil. Where isolations were
made from mycelium, care was taken in every case to observe microscopically that
the fungal colony resulting from the isolation grew directly from mycelium estab-
lished on the cellulose. The soil samples in which cover slips were buried were kept
at laboratory temperatures, and moisture content fluctuated between about 40-60%
of moisture-holding capacity.

The localities and the soils in which some study has been made were as follows:

(1) Black fen peat, pH 7-0, arable, Stretham, Cambridgeshire.

(2) Calcareous loam, pH 7-2, arable, Cambridge.

(3) Loamy sand, pH 6:8, arable, University Farm, Cambridge.

(4) Weathered chalk, pH 7:6, side of a quarry, Cambridge.

(5) Leaf litter, pH about 5-2, under conifers and acid sandy soil (pH about 4-4)
underlying litter, Santon Downham in the Breckland, Suffolk.

(6) Gault clay, arable, University Farm, Cambridge.

(7a) Sandy loam, pH 7-5, arable, Hildersham, Cambridgeshire.

(7b) Sandy loam, under grass, Hildersham, Cambridgeshire.

(8) Mull, pH 7-0, under mixed-leaf litter, North Gower, Ottawa, Canada.

These soil samples were put through a 3-mm. sieve before use (No. 5 was not
sieved, and No. 8 was coarsely sieved).

Before discussing individual fungi, a brief description of the course of
decomposition of cellulose film as it related to broad groups of soil
organisms will be given. In general, the process is as follows: Shortly
after burial in soil, fungi develop on the film. Chytrids are frequent
early colonists, but owing to their mode of growth, with limited spread
of rhizoids, they are not of much importance in cellulose breakdown
unless present in large numbers. Filamentous fungi appear at the same
time. Most of these grow over the surface of the film, and put down
numerous ‘rooting’? or ‘nutritional’ branches into the thickness of
the cellulose sheet. Sometimes these ‘rooting’ branches obviously
secrete a cellulase enzyme, dissolving out visible cavities around the
branches, but more usually enzymic action is restricted and no such
cavities can be seen. Later the branches extend considerably. Other
filamentous fungi may grow over the surface of the film without
development of ‘roots’. Visible zones denoting solution of cellulose
may occasionally be noted surrounding these hyphae, but more usually
they are not visible. After a variable period of time, of the order of
a few weeks, mycelium becomes moribund and bacteria develop over
it, and over apparently undecomposed cellulose in large numbers.
Whether these include true cellulose-decomposing bacteria is uncertain.
Bacteria which directly decompose the cellulose contribute little to its
breakdown during the early stages before fungal action. The bacteria
invariably support a population of nematodes and sometimes patches of
amoebae. The nematodes are often parasitized by predacious fungi.
These appear to be the only fungi developing over the bacterial debris;

248 H.T. TRIBE

no fungi seem to live on moribund bacterial cells. If no larger soil fauna
appear, this condition persists indefinitely up to at least six months.
Frequently, however, microbial tissue and cellulose are consumed by
soil animals. So far, mites, collembolans, and enchytraeid worms have
been found. The first two produce well-defined excremental pellets con-
sisting of microbial tissue and (presumably) undecomposed cellulose.
Mites were found to predominate in the litter and acid sand soil studied,
eventually converting the cellulose into masses of pellets. Enchytraeid
worms mix up the residues with a large proportion of soil, and their
excreta is difficult to distinguish from small soil particles (Kubiena,
1955). They will remove all traces of cellulose from the cover slip on
which it is mounted, and since they may be 1 cm. or more in length will
deposit the excreta away from the cover slip into the soil. Enchytraeid
worms have so far been found in one sample of fen soil, in both samples
of sandy loam, and in the mull. They can often be seen in the soil from
the time of burial of the cellulose film, but do not attack it until microbial
tissue has replaced part of the cellulose, perhaps after 5-8 weeks.
Sometimes young enchytraeids have been found which have probably
originated on the film. Further decomposition of residual cellulose in
excremental pellets has not been studied. Earthworms have not been
found so far—possibly because of sieving the soil samples before use..

Thus the fungi are of importance in the early stages of decomposition,
as has often been surmised, and become moribund after perhaps 2—6
weeks, or longer in the chalk or litter soils. It should be noted, however,
that cellulose film is quite thin (about 55), and differs in this respect
from some forms of natural cellulose. Fungi would certainly persist
longer in thicker substrates.

Having outlined the general manner in which cellulose film is decom-
posed under aerobic conditions, I shall now consider some of the fungi
found in relation to the decomposition process. A few fungi which were
not found but which one may have expected to find will also be con-
sidered, since their absence may have ecological significance.

Chytrids were frequently observed on cellulose film, particularly when
it was buried in soils No. 1, 3, and 7. No attempt was made to study
chytrids in any detail. ‘Cellophane’ has often been used as a bait for
isolation of these fungi, from ponds and ditches (Haskins, 1946) and
from soil (Sparrow, 1957).

Filamentous fungi occurring most frequently on cellulose film buried
in the arable soils were those which put the characteristic ‘rooting’
branches into the film. Isolates consisted of Botryotrichum piluliferum
Sacc. and Marsh. (soil samples No. 1, 2, 3, and 6), Humicola grisea

DECOMPOSITION OF BURIED CELLULOSE FILM 249

Traaen (soils No. 2, 3, and 6), and one resembling B. piluliferum (soils
No. 7 and 8).

B. piluliferum has been fully redescribed as a strong cellulose-decomposing fungus,
several strains of which are maintained in the Quartermaster Collection of micro-
organisms (White & Downing, 1951). This is a collection of micro-organisms
believed to be of importance in spoilage of stored materials. It has rarely been
recorded from soil. It was found in Manitoba soils by Bisby, James, & Timonin
(1933), and from filter-paper from certain neutral soils by Jensen (1931) as Cocco-
spora agricola. Downing (1953) proved that Coccospora agricola Goddard was the
same fungus as B. piluliferum, whose essential characteristics were hyaline globose
spores of 10-25 diam. and rough olivaceous hairs. She further discovered the
presence of‘microconidia, borne on simple phialides, which had not been recorded in
the original description of B. piluliferum. In culture, aleuriospores are typically borne
in raceme-like clusters or on short side branches; on cellulose in soil they usually
appear quite late as isolated spores, probably abstricted from the sides of hyphae on
tiny evanescent papillae. Sometimes they are produced in this way in slide cultures,
and then are not, by definition, aleuriospores. It is not possible to identify this
species with certainty on cellulose film with the microscope.

Humicola grisea Traaen is characterized by production of dark, typically globose
aleuriospores 12-17 diam. It also has recently been described by White & Downing
(1953). It is recorded as a powerful cellulose-decomposing fungus, and is known
only from soils, decaying wood, and other coniferous and hardwood débris in or on
the soil. Like B. piluliferum, it is not known to form a perfect stage. H. grisea
(Traaen) is synonymous with Monotospora dalae Mason, Mycogone nigra (Morgan)
Jensen, Basisporium gallorum Moll., and Melanogone puccinioides Wollenweber &
Richter. Microconidia, similar to those found in B. piluliferum were recorded, but
only in one of seven isolates studied by White & Downing. When growing on
cellulose in soil, it sometimes spreads over the surface of the supporting glass cover
slip on which it produces large numbers of its spherical brown spores. It can then
be identified microscopically from the slide.

The isolates resembling B. piluliferum obtained from soils No. 7 and 8 often bore
chlamydospores on the ‘rooting’ branches in the cellulose film. The aerial mycelium
was bright orange and a red ‘plum-juice’ coloured pigment was produced in Czapek-
Dox agar. The isolate from soil No. 7 produced some olivaceous hairs, but that
from soil No. 8 was less deeply pigmented and did not produce hairs.

I must add here that none of my isolates of the above-mentioned species have ever
produced microconidia. Another fungus, isolated from soils No. 1, 2, 4, 6, and 7
would, however, produce no aleuriospores, but only microconidia on tiny phialides
as described for B. piluliferum and H. grisea. Some isolates of this fungus formed
imperfect perithecia on potato dextrose agar. Both phialides and imperfect peri-
thicia have occasionally been found on cellulose film in situ, and on one slide made
from cellulose film buried in weathered chalk these were associated with a Chaeto-
mium perithecium. There is evidence that this isolate is an imperfect Chaetomium,
because similar colonies were obtained from ascospores from a perithecium of
C. elatum Kunze, a number of which had developed on filter-paper laid on top of the
chalk. Twenty-one spores from this perithecium were picked out on to Czapek-Dox
agar. Only two of these spores germinated, close together, and the resulting colony
was indistinguishable from the microconidial isolates in form, pigmentation,
microconidial production, and in eventual formation of imperfect perithecia.
V arious media including those with added paper or straw failed to induce proper
Perithecial formation in any isolate, nor were they formed at the edges of various
isolates when grown together. Neither Chivers’ monograph (1915), nor Skolko

250 H.T. TRIBE

and Groves’ treatments of Chaetomium species (1948, 1953) mention microconidia
as being present, but Mason (1933) figures an illustration from Zopf for C. globosum
showing these, and Bainier (1909) figures them for C. elatum, and states they were
present in large numbers when C. elatum was grown on any of three substrates.
Although perithecia of Chaetomium have only twice been seen on slides of buried
‘Cellophane’, it thus appears likely that a species of this genus is present in an
imperfect form. There appears to be a similarity between at least two species of
Chaetomium and the aleurispore-forming genera. C. seminudum (Ames, 1949)
produces chlamydospore-like bodies, 10-15 diam., usually on the ends of short,
slender stalks. Hair-like structures which resemble the perithicial hairs may be
scattered on the agar surface, C. homopilatum (Omvik, 1955) also produces aleurio-
spores, of rather smaller size, in beer-wort agar, together with intercalary chlamydo-
spores. Omvik’s species, with another new Chaetomium and a new species of
Humicola, were isolated from filter-paper from a Norwegian soil.

I think that all these isolates from ‘Cellophane’ form a natural group,
at least having greater similarities among themselves than with the other
fungi to be described.

An entirely different fungus which produced typical ‘roots’ occurred
in the weathered chalk only (No. 4). This was a species of Stysanus,
found co-dominant with the microconidial isolate mentioned above on
cellulose in the chalk. Typical coremia and an Echinobotryum stage
(Mason, 1933) were developed on the cellulose film. It was once isolated
from fen soil, but not seen sporing on ‘Cellophane’.

Stachybotrys atra Corda was found, rather sporadically, in soils No. 1,
2, and 3. It is readily identified microscopically (Bisby, 1943), and can-
not be missed on examination of a slide. It differs from the fungi men-
tioned above in morphology of the ‘rooting branches’, the fungus
growing through the cellulose as single hyphae and dissolving out long
narrow cavities. Smith (1954) notes this species to decompose cellulose
rapidly in the presence of small amounts of mineral nutrients. It has
been frequently isolated from exposed cotton fabrics (Siu, 1951, p. 336),
and has been frequently isolated from soils.

The closely related Memnoniella echinata (Rivolta) Galloway, also a
destructive fungus and unlikely to be missed, has not been seen on
‘Cellophane’. Its ecology has been thoroughly discussed by White et al.
(1949), who concluded that it was a tropical species whose preference
was for the purer forms of cellulose. On the basis of direct examination,
it was seen on paper and fabrics in the tropics more frequently than any
other single species. Fungi mostly associated were Gliomastix convoluta
and Stachybotrys atra, and perithecia of Ascotricha and Chaetomium.
White et al. also showed that it acted upon cotton fibres by growing
over the surface, and at intervals sending down short sucker-like branches
which were seen extending into dissolved-out pockets. They stated
Myrothecium verrucaria and Humicola sp. gave similar results, which

DECOMPOSITION OF BURIED CELLULOSE FILM 251

shows their action and growth form is not dissimilar from that of
Humicola sp., at least on cellulose film.

Myrothecium verrucaria (Alb. and Schw.) Ditm. ex Fr. (= Metar-
rhizium glutinosum Pope (White & Downing, 1947)) is another cellulose-
decomposing fungus not found so far on cellulose film. It is considered
by Siu (1951) to be about the most powerful cellulose-destroying fungus
known in the laboratory, but is practically never observed fruiting or
growing on cotton fabrics in the field, although it has been isolated quite
a few times, probably as surface contaminants (p. 159). Species of
Myrothecium are not infrequently recorded in lists of soil fungi.

A number of mycelia sterilia have been isolated from time to time,
especially from soils No. 2, 3, 7, and 8. One of these from soil No. 3 was
powerfully active on cellulose in the soil, putting coarse ‘rooting’
branches into the film. These branches tended to autolyse, leaving large
cavities. The fungus grew quite sparsely in culture on Czapek-Dox agar,
but would not attack cellulose film if the latter were placed on the agar
surface. This was in contrast to the behaviour of the aleuriospore and
microconidial isolates, which put down the usual ‘rooting’ branches into
‘Cellophane’ laid on agars.

From soils 7a and 8, mycelium identified as Rhizoctonia solani
Kühn was found to be dominant. It grew vigorously over the film, acting
upon it directly without ‘roots’. A mixture of equal parts of soils No. 3
which contained no Rhizoctonia with No. 7a resulted in 100% coloniza-
tion of added cellulose by Rhizoctonia. The ‘rooting’ forms present in
soil No. 3 were active, but Rhizoctonia was much more vigorous,
having larger hyphae and a faster growth rate, and overgrew them.
Occurrence of this fungus on cellulose film was unexpected.

Blair (1943) showed that his isolates of Rhizoctonia had only weak cellulose-
decomposing activity as measured on agar plates containing precipitated cellulose.
Species of Penicillium, Trichoderma, Helminthosporium, and Fusarium were used
for comparison. None of his isolates grew over filter-paper laid on water agar and
saturated with a mineral nutrient solution. It is possible, however, that like the
Sterile isolate from soil No. 3 mentioned above, it may be active on cellulose only
under certain conditions. Blair found that his strains of Rhizoctonia grew through
soils at a rate of about 1 cm. per day, and that removal of the agar inoculum after
2 days had practically no effect on this growth rate. He found that addition of 1%
(w/w) ground wheat straw, lucerne meal, or grass meal depressed spread to about
one-third, attributing this to poor cellulose-decomposing ability, and also partially
to nitrogen starvation and to fungistatic carbon dioxide produced by micro-organ-
isms decomposing the organic matter. Again, it is conceivable that Rhizoctonia
hyphae were investing this.material in preference to spreading through the soil.

Isolation to culture from cellulose film from soil No. 8 proved to be difficult.
Pieces of ‘Cellophane’ seen to be extensively colonized were plated on to Czapek-
Dox agar. Often the hyphae autolysed completely. If they survived, they grew very

252 H.T. TRIBE

slowly on to the agar. In some platings, spores of a species of Mucor were present,
and in every case had germinated and formed colonies 1-5 cm. in diameter, while
the Rhizoctonia had just grown off the film. Experiences of this kind demonstrate
the need of microscopic observation. The isolates grew rather better on soil extract
agar, and certain transfers to this medium grew away, and when inoculated into
sterilized soil containing ‘Cellophane’ pieces grew rapidly over these, entirely
destroying the strength of the pieces in 2-3 weeks. Growth and appearance were
exactly as on ‘Cellophane’ in the original unsterile soil. It is obvious that this fungus,
though its hyphae were morphologically very similar to those of R. solani, possessed
physiological properties quite dissimilar from normal isolates of R. solani.

Rhizoctonia comes into contact with ‘Cellophane’ in these soils by means of
hyphae travelling through the soil, probably originating from sclerotia or resistant
hyphae. Warcup (1957) obtained Rhizoctonia from a wheat-field soil from both
these sources, and illustrates resistant hyphae showing new growth in agar. He
noticed that both Rhizoctonia solani and a sterile fungus appeared most abundantly
during the period of decomposition of straw in the soil he was studying, but he was
uncertain whether these fungi played any part in the decomposition. Until quite
recently R. solani has rarely been isolated from soil by dilution- and soil-plate
techniques, but by methods favouring hyphal isolation it can readily be obtained
(Thornton, 1956; Warcup, 1957).

It is a matter of interest that R. solani developing vigorously on cellulose film was
not attacked by Trichoderma viride Pers. ex Fries, nor indeed was the cellulose film.
Certain isolates of this fungus have cellulose-decomposing activity in the laboratory;
as, for example, on cotton sheeting (Reese et al., 1950). White states, however, that
direct examination of hundreds of cotton fabric samples in various stages of decay
from nearly all parts of the world did not reveal any fruiting structures of T. viride
on the fabric. T. viride was considered to exist on the samples much like other spores
which had been deposited with the dust of the atmosphere (White, in Siu, 1955,
p. 159). T. viride was isolated from cellulose film in the acid litter, but not from any
other soil studied. Even on ‘Cellophane’ in litter it was not dominant. It is known
that T. viride is more active against other fungi in environments of low pH, against
for example R. solani (Weindling & Fawcett, 1936) and Fomes annosus (Rishbeth,
in Garrett, 1956), and that it grows well in soils which have been sterilized (Warcup,
1951; Mollison, 1953). In ordinary neutral soils, however, from which it is usually
readily isolated, its ecological niche remains a mystery. The perfect stage is Hypocrea
rufa, in which form it appears on dead wood and stems, often accompanied by the
Trichoderma stage (Bisby, 1939).

Sporotrichum (or Aleurisma) species were commonly associated with
‘rooting’ forms in soils No. 1, 3, and 6. They were not primary cellulose-
decomposing fungi, but appeared when the other had become estab-
lished.

Gliomastix convoluta was found occasionally.

Penicillium spp. have never been seen sporing on cellulose film
(exceptin soil No. 5), but some were once isolated from thinly covering
mycelium on ‘Cellophane’ from fen soil.

In the coniferous litter and the underlying acid sand (No. 5), the
microflora developing on buried cellulose film was entirely different
from that on the arable soils or the mull. None of these species were
found; instead, species of Oidiodendron Robak and Geomyces Traaen

DECOMPOSITION OF BURIED CELLULOSE FILM 253

were dominant, and a species of Penicillium was seen sporing on the
film. Trichoderma was isolated occasionally from ‘Cellophane’ in litter.
The combination of Oidiodendron spp. and mites resulted in total dis-
integration of the cellulose film in some 12 weeks. Oidiodendron spp.
were first described on wood pulp (Robak, 1932). They are increasingly
being reported in soil lists, probably as they become better known.
Further study is necessary on cellulose in a litter environment. There
are probably numbers of Basidiomycetes to be found (Lindeberg, 1946).

Returning to arable soils, mention must be made of predacious fungi
found parasitizing nematodes. These fungi have recently been reviewed
by Duddington (1957), together with a discussion on their ecology.
Species prodiicing mycelial networks (soils No. 3 and 8), constricting
rings (soil No. 6), adhesive knobs (soil No. 8), and in soil No. 6 an
obligate parasite, Harposporium sp. (kindly identified by Mr. D. C.
Twinn, The Nature Conservancy, Grange-over-Sands, Lancs.), have
been seen on cellulose film. Occasionally spores have been associated
with these, probably belonging to the genera Arthrobotrys and Dactyl-
ella. The species producing constricting rings was abundant in the clay
soil sample after 12—18 weeks burial of the ‘Cellophane’. Although these
are in no sense cellulose-decomposing fungi, they have been caused to
develop through addition of pure cellulose to the soils. In his review
Duddington says that ‘it is a little surprising, when we consider the
richness of the soil predacious fungus flora, that they do not play a
larger part in published lists of soil fungi’. He suggests this is partly due
to their failure to appear on isolation plates in absence of suitable prey,
when they cannot compete with the more vigorously growing moulds,
and partly to the unsuitably low pH of many isolation media.

By way of summary it is of interest to briefly examine the dominant
filamentous fungi which developed in the different soils studied. A
number of pieces of cellulose film buried in a soil sample mean that the
cellulose is virtually offered to the whole variety of population of that
sample. In the nearly neutral arable soils (No. 1, 2, 3, 6, and 7), though
very diverse in texture and composition, the fungi which were normally
dominant belonged to the ‘rooting’ group, viz. Botryotrichum, Humicola,
and the microconidial isolates. The different species of this group were
able to co-exist on the same piece of cellulose. If, however, Rhizoctonia
were present in a soil, together with species of the ‘rooting’ group, as in
soils 7a, 8 and the mixture of 7a and 3, it usually overgrew these. It had
&rcater competitive saprophytic ability than the ‘rooting’ species—this
expression is defined as the summation of physiological characteristics
(Possessed by a fungus) that make for success in competitive coloniza-

254 H.T. TRIBE

tion of dead organic substrates (Garrett, 1956). On account of its larger
hyphae and faster growth rate, it rapidly colonized the cellulose film,
rendering the film in condition for development of the bacterial stage.
This was presumably through excretion from the hyphae, autolysis, and
enzymic softening of the substrate. In soil No. 8, certain pieces of
‘Cellophane’ remained untouched for a period of several weeks, by
which time those originally attacked by Rhizoctonia or by a ‘rooting’
fungus were extensively colonized. Presumably, therefore, neither of these
fungi happened to be near to the untouched pieces, and none of the
other fungi in contact were able to develop on the cellulose.

Stachybotrys had the capacity to become dominant or co-dominant
with the ‘rooting’ fungi, which it occasionally was in soils No. 1 and 3.
Its occurrence was, however, sporadic; presumably it was not abundant
in the soils.

In weathered chalk (soil No. 4) Stysanus was co-dominant with a
‘rooting’ fungus. Stysanus was either not present in the other soils or
required relative freedom from competition. It was noteworthy that
few bacteria developed on cellulose film in this soil, despite the high
pH, probably because there was little organic matter present. Develop-
ment of the bacterial stage did not occur to its usual extent, even by 10
weeks they were quite few, and this may have allowed the big coremia
of Stysanus to develop fully on the ‘Cellophane’.

In the litter sample, end also in the acid sand (which was practically
devoid of organic matter and hence probably received its microflora
from the litter layer above it), the fungi found were quite different.
Species of Oidiodendron and the closely related Geomyces were domin-
ant. A species of Penicillium was present, and was seen sporing on some
pieces of ‘Cellophane’. It is probable that the dominants recorded from
the arable soils were absent, though it is conceivable that they were
present and inactive. Conversely, were Oidiodendron spp. present in the
other soils? I should doubt whether Oidiodendron spp. would compete
successfully with the dominants in the arable soils, as the former were
comparatively slow to develop.

As far as the arable soils are concerned, these results are in agreement
with those of Jensen (1931), concerning the fungus flora of straw buried
in neutral soils. He did not record Rhizoctonia, but this would not have
been revealed by his plating method had it been present. Certain fungi
commonly recorded on straw by other workers have not been seen on
cellulose film, species of Fusarium (especially F. culmorum), Aspergillus,
Penicillium, and Trichoderma. F. culmorum definitely colonizes straw
from soil (Butler, 1953). Penicillium and Trichoderma have been recorded

DECOMPOSITION OF BURIED CELLULOSE FILM 255

from straws after thorough washing and surface sterilization procedures
by Sadasivan (1939) and Walker (1941). Species of all these moulds
possess cellulose-destroying power (Norman, 1930; Reese et al., 1950;
Siu, 1951). Perhaps Penicillium and Aspergillus species are more charac-
teristic of growth on cellulose in damp environments which are better
aerated than the average soil—it is possible they may grow on cellulose
film exposed under such conditions above ground. On the other hand,
the presence of encrusting substances along with the cellulose may be
expected to stimulate a richer microflora than would arise on pure
cellulose.

To conclude, methods combining the techniques of microscopic
observation and isolation of the fungi seen to be present on particular
substrates buried in soils seem to me to show promise in furtherance of
knowledge of fungal ecology. All substrates are not as favourable for
this purpose as ‘Cellophane’, but with a certain experimental ingenuity
these techniques should be capable of extension to numbers of other
substrates.

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